The metallocene complex is a compound used as one of catalyst components for various polymerization reactions, and a complex compound having one or more cyclopentadienyl groups or derivatives thereof each bound to the central metal. In particular, the metallocene complex having one cyclopentadienyl group or derivative thereof bound to the central metal is referred to as a half metallocene complex in some cases.
As the metallocene complex having gadolinium (Gd) as a central metal, there have been known bis(pentamethylcyclopentadienyl)gadolinium borate, dimethylaluminum (μ-dimethyl)bis(pentamethylcyclopentadienyl)gadolinium, and the like. It has been known that those metallocene complexes are used as components of polymerization catalyst compositions (for example, refer to Patent Document 1).
In addition, as a lanthanoid metallocene complex having a bis(trimethylsilyl)amide ligand, there have been known: one having cerium (Ce) as a central metal (refer to Non-Patent Document 1); one each having yttrium (Y), lanthanum (La), or cerium (Ce) as a central metal (refer to Non-Patent Document 2); and one having neodymium (Nd), samarium (Sm), or ytterbium (Yb) (refer to Non-Patent Document 3).
All of those lanthanoid metallocene complexes each having a bis(trimethylsilyl)amide ligand have a tetramethyl cyclopentadiene ligand.
On the other hand, there have conventionally been many proposals for the polymerization catalyst for conjugate diene polymerization.
For example, it has been known that high cis-1,4-bond conjugate diene polymers are obtained by using a composite catalyst system containing a neodymium compound and an organic aluminum compound as main components. Part of those polymers has been industrially used as a polymer catalyst system for butadiene (for example, refer to Non-Patent Documents 4 and 5).
In addition, it has been reported that the high cis-1,4-bond conjugate diene polymer can be obtained by using a catalyst system containing the above dimethylaluminum (μ-dimethyl)bis(cyclopentadienyl) gadolinium and the like (refer to Patent Document 1).
However, there has been demanded a method of producing effectively a conjugate diene polymer having a high content of cis-1,4-structures in a micro structure, a high molecular weight, and a sharp molecular weight distribution, and hence development of a polymerization catalyst therefor has been demanded.
Patent Document 1: JP 2004-27179 A
Non-Patent Document 1: Organometallics, 1989, 8, 2637-2646
Non-Patent Document 2: Journal of Organometallic Chemistry, 364 (1989) 79-86.
Non-Patent Document 3: Inorg. Chem. 1981, 20, 3267-3270
Non-Patent Document 4: Macromolecules, 15, 230, 1982.
Non-Patent Document 5: Makromol. Chem., 94, 119, 1981.